This invention is generally directed to an apparatus or device, and processes for the preparation of carrier particles and developer compositions thereof; and more specifically, the present invention relates to the preparation of coated carrier particles by the selection of magnetic field agitation. In one embodiment of the present invention, coated carrier particles are supplied to a known kiln by magnets attached to, for example, a continuous transporting means positioned external to the kiln, which magnets attract, subsequently release, and agitate the carrier mixture in the kiln permitting, for example, the avoidance or minimization of agglomeration thereby enabling better flow characteristics for carrier particles. With present carrier devices and processes, there can be formed an undesirable mass. More specifically, with many present carrier processes and devices the carrier can be subject to problems of bead sticking, undesirable adhesion of carrier beads to a kiln wall within which they are contained projection caused by the melting of polymer carrier coatings, sluggishness and poor flow causing loss of particle size control, product nonuniformity, and in some instances total process termination. Bead sticking can be caused, for example, by adhesion of the carrier beads to each other caused by, for example, melting polymer coatings. The aforementioned and other problems are avoided or minimized with the devices and processes of the present invention. The carrier particles prepared with the devices and processes of the present invention can be comprised of a core with a coating comprised of a mixture of polymers enabling insulating particles with relatively constant conductivity parameters, and also wherein the triboelectric charge on the carrier can vary significantly depending on the coatings selected. Developer compositions comprised of the aforementioned carrier particles and toner particles are useful in electrostatographic or electrophotographic imaging systems, especially xerographic imaging and printing processes. Additionally, developer compositions comprised of substantially insulating carrier particles prepared in accordance with the process and devices of the present invention can be useful in imaging methods wherein relatively constant conductivity parameters are desired. Furthermore, in the aforementioned imaging processes the triboelectric charge on the carrier particles can be preselected depending on the polymer composition applied to the carrier core.
Carrier particles for use in the development of electrostatic latent images, and processes for the preparation thereof are described in many patents including, for example, U.S. Pat. No. 3,590,000. These carrier particles may be comprised of various cores, including steel, with a coating thereover of fluoropolymers; and terpolymers of styrene, methacrylate, and silane compounds. These carrier particles can be prepared by, for example, solution coating methods.
There are also illustrated in U.S. Pat. No. 4,233,387, the disclosure of which is totally incorporated herein by reference, coated carrier components for electrostatographic developer mixtures comprised of finely divided toner particles clinging to the surface of the carrier particles. Specifically, there is disclosed in this patent coated carrier particles obtained by mixing carrier core particles of an average diameter of from between about 30 microns to about 1,000 microns with from about 0.05 percent to about 3.0 percent by weight, based on the weight of the coated carrier particles, of thermoplastic resin particles. The resulting mixture is then dry blended until the thermoplastic resin particles adhere to the carrier core by mechanical impaction, and/or electrostatic attraction. Thereafter, the mixture is heated to a temperature of from about 320.degree. F. to about 650.degree. F. for a period of 20 minutes to about 120 minutes, enabling the thermoplastic resin particles to melt and fuse on the carrier core. Dry coating carrier processes are also illustrated in U.S. Pat. Nos. 4,937,166 and 4,935,326, the disclosures of which are totally incorporated herein by reference. Subsequent to the aforementioned dry coating, the carrier particles can be introduced into a kiln for the primary purpose of ensuring the permanent fusing and fixing of the polymer coatings to the carrier core. The aforementioned kiln process, especially at high polymer coating weights, for example of 3 percent, results in some instances in the disadvantages of bead sticking, sluggishness, and carrier particles with poor flow. Poor flow of carrier can be caused by bead sticking, and can result in nonuniform temperature profiles when heating the carrier core and carrier polymer or polymers, and the like. These and other disadvantages are minimized or avoided with the devices and processes of the present invention.
In a patentability search report the following U.S. Pat. No. were recited: 4,223,085 which discloses nickel carrier particles wherein a furnace, such as a rotary kiln, may be employed to heat treat the carrier, which carrier may be agitated, see for example column 5, lines 22 to 38; U.S. Pat. No. 4,478,925 discloses the preparation of magnetic carrier particles by agitating a dry mixture of carrier particles and resin particles in a magnetic field, followed by heating of the aforementioned mixture, reference the Abstract; in a preferred process embodiment, see column 4, of the '925 patent there is described an apparatus with a housing or container in which are mounted one or more cylindrical roller members which rotate coaxially about a set of stationary magnets arranged within the roller member, referred to as a sleeve or shell; a supply of developer is placed within the housing and is attracted magnetically to the surface of the rotating roller with agitation of the mixture of carrier particles and toner particles occurring as the rollers rotate about the magnets in the housing; and U.S. Pat. No. 4,283,438, which discloses a method for encapsulating magnetic particles by enclosure within oil drops, mixing in an aqueous solution and dispersing the oil drops with the enclosed particles by application of an alternating magnetic field.
Other patents relating to carriers and processes for the preparation thereof include, for example, U.S. Pat. No. 3,939,086, which teaches steel carrier beads with polyethylene coatings, see column 6; U.S. Pat. No. 4,264,697, which discloses dry coating and fusing processes; U.S. Pat. Nos. 3,533,835; 3,658,500; 3,798,167; 3,918,968; 3,922,382; 4,238,558; 4,310,611; 4,397,935 and 4,434,220.